1. Field of the Invention
A trap material is provided for use in a chemical trace detection portal for detecting trace amounts of contraband. The trap material is made of aluminum foam metal which has a high thermoconductivity and reduced density as compared to conventional trap materials, thereby ensuring that the internal temperature of the improved trap rapidly achieves the temperature required during desorbing of the trace materials.
2. Description of Related Art
Atmospheres have been sampled for the presence of targeted substances for many decades. In particular, the requirement to detect vapors and particles emitted from contraband materials has led to many improvements in sample harvesting and pre-concentration. As an example, reference is made to U.S. Pat. No. 4,242,107 which issued to Anthony Jenkins on Dec. 30, 1980 and is entitled “Apparatus for the Separation of a Constituent From an Atmosphere.” In U.S. Pat. No. 4,242,107 there is disclosed an apparatus for sampling an atmosphere for the presence of a constituent in which a flow of the atmosphere is first drawn through a trap capable of releasably absorbing the constituent and the trap is then passed through a carrier gas stream which removes and conveys the constituent into a detector. The trap may comprise a rotatable disc of wire mesh which cuts continuously across a flow of the atmosphere and a carrier gas flow. The volume flow rate of the atmosphere is greater than that of the carrier gas thereby giving a large concentration gain of the constituent in the carrier flow. The apparatus can be used for detecting the presence in the atmosphere of vapors emanating from explosives and for this purpose the carrier gas flow can be directed into an electron capture detector.
The characteristics which are essential for good trap design are: (1) the trap must allow a high flow of air through the material; (2) the trap must trap small particles at the micron level; (3) the trap must have high surface area to trap low volatility vapors; (4) the trap must be strong enough to maintain the pressure drop across the trap necessary to support the high flow requirements; (5) the trap must allow heating to temperatures in excess of 200° C.; and (6) the trap must have a low volume so that the trap can be purged by the low carrier flow within a short time, usually less than one second.
Various materials have been used in the past for the collection and detection of explosives and illicit drugs. Metal gauzes, metal felt blanket, paper, and artificial fiber felts are among the materials that have previously been employed for this purpose.
A new challenge has recently been imposed on top of the already challenging requirements of detecting drugs and explosives in large volumes of air. This is provided by the need to rapidly detect explosives and narcotics on passengers traveling through airport security checkpoints.
U.S. Pat. No. 6,073,499, which issued to Gary S. Settles on Jun. 13, 2000 and is entitled “Chemical Trace Detection Portal Based on the Natural Air Flow and Heat Transfer of the Human Body” discloses a portal provided for use with a detector for detecting trace amounts of contraband that may be retained on skin or clothing of the human subject.
The portal disclosed in U.S. Pat. No. 6,073,499, relies upon the continuous process by which microscopic flakes of skin continuously separate from human subjects. The portal further relies on the existence of a human thermal plume consisting of a layer of warm air adjacent to all human subjects. The warm air rises in the cooler surrounding air and transports the microscopic flakes of skin upwardly. The portal capitalizes on this phenomenon by providing at least a partial enclosure with a funnel-shaped collector above the human subject. A low speed fan of relatively dense cool air may be introduced into the portal to buoyantly lift the warmer air of the human thermal plume upwardly. The air stream defined by the human thermal plume and the skin particles thereof moves to a trap in the funnel-shaped collector of the portal. The trap cooperates with a detector for detecting the presence of molecules of interest.
In a portal system, as disclosed in U.S. Pat. No. 6,073,499, the trap must be heated very rapidly to temperatures of about 200° C. in order to desorb and volatize the trap material. The speed at which this can be achieved is critical to the success of the test, since delays at the checkpoint cannot be accommodated in many airports.